A liquid crystal display device includes a TFT substrate and a color filter substrate. The TFT substrate is configured such that pixel electrodes, thin film transistors (TFTs), and the like, are arranged in a matrix form. The color filter substrate is disposed opposite to the TFT substrate, in which color filters, and the like, are formed at locations corresponding to the pixel electrodes of the TFT substrate. A liquid crystal is interposed between the TFT substrate and the color filter substrate. Then, an image is formed by controlling the transmittance of light of the liquid crystal molecules for each pixel.
The liquid crystal display device can be made small and thin, and is used in a wide range of applications such as mobile phones or other electronic devices. In recent years, various types of applications have been added to the mobile phone. Also, the input device is expected to have a function allowing finger input through a touch panel, in addition to the conventional key-button operation. In this case, a touch panel is attached on the side of the color filter substrate of the liquid crystal display panel.
There is a strong demand not only for reducing the overall size of the liquid crystal display device as a set, but also reducing the thickness of the liquid crystal display panel, while the size of the screen remains unchanged. In order to meet the demand for a thin liquid crystal display panel, a liquid crystal display panel is produced, and then the outside of the liquid crystal display panel is polished to a desired thickness. The liquid crystal display panel is formed by the TFT substrate having pixel electrodes, thin film transistors (TFTs), and the like, and by the color filter substrate having color filters. The two substrates constituting the liquid crystal display panel are glass substrates that are standardized, for example, to a thickness of 0.5 mm or 0.7 mm. It is difficult to obtain such standardized glass substrates from the market. In addition, very thin glass substrate has a problem relating to mechanical strength and bending in the production process, leading to a reduction in the production yield. For this reason, the liquid crystal display panel is formed by the standardized glass substrates, and then the outside of the liquid crystal display panel is polished to a desired thickness.
The reduction of the thickness of the liquid crystal display panel poses a problem of the mechanical strength.
When a mechanical stress is applied to the display surface of the liquid crystal display panel, there is a risk that the liquid crystal display panel will be destroyed. The situation is the same with the liquid crystal display panel on which the touch panel is placed, due to the small thickness of the touch panel.
In order to prevent the liquid crystal display panel from being destroyed by an external force, a front window of resin or glass is attached to the screen side of the liquid crystal display panel. In this case, an air layer is present between the liquid crystal display panel and the touch panel, or between the touch panel and the front window. The transmittance of the light from the backlight is reduced by the reflection from the interface in this area.
In order to prevent this, JP-A No. 83491/2008 describes a configuration in which an adhesive layer or an anti-reflection coating is formed between the liquid crystal display panel and the touch panel, or between the touch panel and the front window. JP-A No. 83491/2008 also describes a configuration in which a main flexible wiring substrate is attached to the liquid crystal display panel in order to connect the liquid crystal display panel to an external circuit, and a touch-panel flexible wiring substrate is attached to the touch panel in order to connect the touch panel to the external circuit. In JP-A No. 83491/2008, the touch panel is of a capacitance type and can function as a touch panel with the front window thereon.
In the capacitance-type touch panel, various operations are possible. However, a touch-panel control IC and touch-panel electronic components are necessary for the touch panel to perform such various operations. In the past, the touch-panel control IC and the touch-panel electronic components have been provided in the touch-panel flexible wiring substrate.
FIG. 11 is a top view of a conventional liquid crystal display device having a front window 200 and a touch panel. In FIG. 11, the front window 200 is shown in the top. The touch panel and the liquid crystal display panel are hidden behind the front window 200, so that they do not appear in FIG. 11. In FIG. 11, a touch-panel flexible wiring substrate 50 is connected to the touch panel, and a main flexible wiring substrate 40 is connected to the liquid crystal display panel.
For example, a black frame 210 is formed by printing in the periphery of the front window 200. The area surrounded by the black frame 210 is a display area 220. In FIG. 11, the touch-panel flexible wiring substrate 50 has a touch-panel electronic component group 51 and a touch-panel control IC 52. Further, the touch-panel flexible wiring substrate 50 also has a terminal portion 53 to connect to the outside. The main flexible wiring substrate 40 has an LCD electronic component group 41 to drive the liquid crystal display panel. Further, the main flexible wiring substrate 40 also has a terminal portion 44 to connect to the outside.
FIG. 12 is a top view of the liquid crystal display panel used in FIG. 11. In FIG. 12, the liquid crystal display panel including a TFT substrate 10 and a color filter substrate 20 is placed on a resin mold 60. An upper polarization plate 21 is attached to the top surface of the color filter substrate 20.
The TFT substrate 10 is made larger than the color filter substrate 20. A terminal area is formed in a portion of the TFT substrate 10 extending beyond the color filter substrate 20. A liquid crystal driver IC 30 for driving the liquid crystal display panel is provided in the terminal area. Further, the main flexible wiring substrate 40 is attached to the terminal area. The LCD electronic component group 41 is mounted on the main flexible wiring substrate 40.
FIG. 13 is a top view of a touch panel 100 to be mounted on the liquid display panel. The touch panel 100 includes a substrate and a wiring portion, as will be described below. The touch-panel flexible wiring substrate 50 is attached to the touch panel 100. The touch-panel flexible wiring substrate 50 has the touch-panel control IC 52 or the touch-panel electronic component group 51. The touch-panel control IC 52 or the touch-panel electronic component group 51 is mounted on the touch-panel flexible wiring substrate 50, so that the touch panel manufacture can determine whether the touch panel 100 is good or bad.
As described above, in the conventional type, the electronic components or the control IC is provided both in the main flexible wiring substrate 40 and the touch-panel flexible wiring substrate 50. Mounting the electronic components or the control IC on the flexible wiring substrates is a process that requires a lot of man-hours. As a result, the production cost of the liquid crystal display device increases. In addition, mounting the electronic components or the control IC on the flexible wiring substrates requires an increase in the size of each flexible wiring substrate itself. As a result, the cost of the flexible wiring substrate increases.